Turbochargers are generally well known in the art. Basically, a turbocharger is a centrifugal air pump that is driven by the engine's exhaust gas. The turbocharger forces an additional amount of air or air-fuel mixture into the engine, which aids in the increase of combustion pressure and engine power. This allows a relatively smaller engine to deliver acceptable fuel economy during normal driving conditions, and to have the increased power characteristics of a larger engine when needed. Turbochargers have been incorporated into both gasoline and diesel engines, for both commercial and passenger vehicle applications.
Examples of turbocharger technology can be found with reference to commonly assigned U.S. Pat. No. 6,089,019 to Roby; U.S. Pat. No. 6,263,672 to Roby et al.; U.S. Pat. No. 6,415,846 to O'Hara; U.S. Pat. No. 6,543,228 to Deacon; U.S. Pat. No. 6,694,736 to Pfluger; U.S. Pat. No. 6,709,160 to Ward et al.; U.S. Pat. No. 6,715,288 to Engels et al.; U.S. Pat. No. 6,802,184 to Huter et al.; and U.S. Patent Application Publication Nos. 2003/0206798 to Allmang et al.; 2004/0037716 to Jaisle; 2004/0062645 to Decker et al.; 2004/0088976 to Jaisle; 2004/0134193 to Klingel; 2004/0194447 to Roby; and 2004/0197212 to Roby, the entire specifications of all of which are expressly incorporated herein by reference.
A recent development in turbocharger technology has been regulated two-stage or sequential turbochargers, in which two relatively smaller turbocharger units are used instead of a single relatively large conventional turbocharger. These regulated two-stage turbocharger systems typically employ a relatively smaller, high-pressure turbocharger unit in series with a relatively larger, low-pressure turbocharger unit.
Unfortunately, conventional regulated two-stage turbochargers still exhibit unsatisfactory characteristics, especially during the overlapping transition period when the turbo speed of the smaller high-pressure turbocharger unit rapidly decreases and the turbo speed of the larger low-pressure turbocharger unit rapidly increases. This phenomenon is believed to be a momentary loss of torque that occurs before the low-pressure turbocharger unit has reached its particular requisite turbo speed. This “drop” in torque during the transition period is quite noticeable and is objectionable to many drivers, especially those driving expensive, high-performance luxury models.
Accordingly, there exists a need for new and improved regulated two-stage turbocharger systems that produce a relatively smooth and unnoticeable transition period between the operation of the high pressure and low pressure turbocharger units.